The directions of the points often vary depending on what particular tradition the spell is coming from. If it has significance to you, and your tradition, use a specific direction. Otherwise, don't worry about it.
The size is similar. The 9 foot dimension is likely used due to the number 3 and the value often attached to it within various sacred traditions (9 is 3, three times). Interpret it as you see fit. Most such works are not exactly like a recipe, where your dough won't rise if you don't do it correctly. It's more a suggestion or interpretation born of experience, or other individuals' work.